1. Field of the Invention
The invention relates to a fluid pressure control circuit. More particularly, the invention relates to a technology for enhancing performance of supplying fluid to/discharging fluid from a fluid pressure device.
2. Description of the Related Art
A fluid pressure control circuit, which includes (a) a fluid pressure device that is operated by a fluid pressure, and (b) a control valve that is connected to the fluid pressure device via a connecting passage, and that changes a rate of flow (hereinafter, referred to as a “flow rate”) of predetermined fluid which is to be supplied to the fluid pressure device or which is to be discharged from the fluid pressure device according to a position of a valve element, is used in, for example, a transmission for a vehicle. A hydraulic pressure control circuit disclosed in Japanese Patent Laid-Open Publication No. 05-196127 is an example of the above-mentioned fluid pressure control circuit. In a control valve of the hydraulic pressure control circuit, a valve element, to which the fluid pressure in a connecting passage is applied via a feedback passage that branches off from the connecting passage, is moved according to a balance between the fluid pressure and a predetermined pressure regulating load. The control valve includes a supply port through which the fluid is supplied from an oil pump or the like, a discharge port through which the fluid is discharged, and a communication port to which the connecting passage is connected. The state of communication (hereinafter, referred to as a “communication state”) among the supply port, the discharge port and the communication port is continuously changed according to the position of the valve element, whereby the flow rate of the fluid to be supplied is controlled.
In such a fluid pressure control circuit, the fluid pressure to be applied to the valve element via the feedback passage does not always reflect the fluid pressure in the fluid pressure device due to resistance generated during circulation of the fluid in the connecting passage (hereinafter, referred to as “circulation resistance of the connecting passage) or the like, when the fluid is being supplied/discharged or the fluid pressure is being changed (hereinafter, referrer to as “during supply/discharge of the fluid or change in the fluid pressure”). Therefore, the flow rate of the fluid which circulates through the control valve is decreased, which makes it difficult to obtain sufficient responsiveness. When such a fluid pressure control circuit is applied, for example, to a fluid pressure device for a transmission (e.g. hydraulic friction engaging device), it is necessary to supply/discharge the fluid promptly during shifting, in order to obtain predetermined shifting responsiveness. Therefore, by increasing the diameter of the valve or by decreasing the valve overlap amount, the cross sectional area of a portion through which the fluid actually circulates in the supply port (hereinafter, referred to as a “circulation cross sectional area of the supply port, the same can be applied to the other ports”), the circulation cross sectional area of the discharge port and the circulation cross sectional area of the communication port are increased. In this case, however, there is a problem that, since the flow rate of the fluid which leaks from the discharge port is also increased, the amount of the fluid to be consumed is increased, which makes it necessary to increase the discharge capacity of the fluid pressure supply source such as an oil pump.